Tolerance ring assembly

ABSTRACT

A tolerance ring having a first axial end, a second axial end, and a central axis, the tolerance ring including an annular band; a plurality of protrusions, all of the plurality of protrusions extending from the annular band; and a guide portion extending from the annular band towards the first axial end of the tolerance ring, where the guide portion includes a guide surface that is curved in an axial section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority under 35 U.S.C.§ 120 to U.S. patent application Ser. No. 16/235,199, entitled “METHODOF USING A TOLERANCE RING,” by Niki S. WOODHEAD et al., filed Dec. 28,2018, which is a divisional of and claims priority to U.S. patentapplication Ser. No. 14/636,550, entitled “METHOD OF USING A TOLERANCERING,” by Niki S. WOODHEAD et al., filed Mar. 3, 2015, now U.S. Pat. No.10,203,004, which application is a continuation of and claims priorityto U.S. patent application Ser. No. 10/552,875, entitled “TOLERANCE RINGASSEMBLY,” by Niki S. WOODHEAD et al., filed Oct. 13, 2005, now U.S.Pat. No. 9,206,853, which was a U.S. national phase application under 35U.S.C. § 371 of International Patent Application No. PCT/GB2004/001681,entitled “TOLERANCE RING ASSEMBLY,” by Niki S. WOODHEAD et al., filedApr. 16, 2004, and claims priority to Great Britain Patent ApplicationNo. 0308957.0, entitled “TOLERANCE RING ASSEMBLY,” by Niki S. WOODHEADet al., filed Apr. 17, 2003, of which these applications are assigned tothe current assignee hereof and incorporated herein by reference intheir entireties. The International Application was published in Englishon Nov. 4, 2004 as WO 2004/094852 A1 under PCT Article 21(2).

BACKGROUND OF THE INVENTION Field of the Disclosure

This invention relates to tolerance ring assemblies, wherein a tolerancering provides an interference fit between parts of an assembly, where afirst part has a cylindrical portion located in a cylindrical bore of asecond part. The invention particularly relates to assemblies having atolerance ring that provides an interference fit between a cylindricalcomponent such as a shaft or a bearing and a housing for the shaft.

Description of the Related Art

Improved engineering techniques have resulted in the need for greateraccuracy of machine parts, raising manufacturing costs. Very closetolerances are required where press fits, splines, pins or keyways areemployed to transmit torque in applications such as pulleys, flywheelsor driveshafts.

Tolerance rings may be used to provide an interference fit between partsrequired to transmit torque. Tolerance rings provide a low cost means ofproviding an interference fit between parts that may not be machined toexact dimensions. Tolerance rings have a number of other potentialadvantages, such as compensating for different linear coefficients ofexpansion between the parts, allowing rapid apparatus assembly, anddurability.

A tolerance ring generally comprises a strip of resilient material, forexample a metal such as spring steel, the ends of which are broughttogether to form a ring. A band of protrusions extend radially outwardsfrom the ring, or radially inwards towards the centre of the ring.Usually, the protrusions are formations, possibly regular formations,such as corrugations, ridges or waves.

When the ring is located in the annular space between, for example, ashaft and a bore in a housing in which the shaft is located, theprotrusions are compressed. Each protrusion acts as a spring and exertsa radial force against the shaft and the surface of the bore, providingan interference fit between the shaft and the housing. Rotation of thehousing or the shaft will produce similar rotation in the other of theshaft or the housing, as torque is transmitted by the tolerance ring.Typically, the band of protrusions is axially flanked by annular regionsof the ring that have no formations (known in the art as “unformedregions” of the tolerance ring).

Although tolerance rings usually comprise a strip of resilient materialthat is curved to allow the easy formation of a ring by overlapping theends of the strip, a tolerance ring may also be manufactured as anannular band. The term “tolerance ring” as used hereafter includes bothtypes of tolerance ring. The term “shaft” as used hereafter includes anyassembly component with a cylindrical portion, such as a shaft or abearing.

Problems can occur during assembly of parts that use tolerance rings. Asthe tolerance ring requires a tight fit in the apparatus, there may beabrasion between the ring and various parts of the apparatus, whichremoves small fragments from the surface of the affected parts. Thesefragments are known in the art as particles. In particular, parts of theprotrusions distal to the band of the ring may generate particles whensliding relative to part(s) of the apparatus. In certain apparatus, suchas a computer hard disk drive where cleanliness is essential, productionof particles is extremely undesirable, as the particles can adverselyaffect the function of the apparatus.

If the material of the housing (e.g. aluminum) is softer than thematerial of the shaft (e.g. steel), it may be desirable to have theprotrusions slide relative to the shaft during assembly to minimiseparticle production. Normally, for this type of arrangement, thetolerance ring's protrusions point inwards.

For apparatus that includes a bearing, however, it may also be desirablethat the bearing has the tolerance ring fitted thereto, and theprotrusions engage the surface of the bearing in the housing i.e. theprotrusions point outwards. The arrangement may be useful where thetolerance ring distributes torque from the housing to the bearing, asload is distributed evenly over a large contact area of the shaftprovided by the tolerance ring. Where the surface area is not maximized,for example when the protrusions engage the bearing under load, theremay be problems with an effect known as “torque ripple” where the torquein the bearing is not generated at a continuous level. It is preferablethat load is distributed over as large an area as possible, for exampleover the base of the protrusions of the tolerance ring.

It may be advantageous to provide in the bore a tolerance ring withoutward protrusions and fit the shaft into the ring. In thisarrangement, although there may be reduced particle production as theprotrusions do not slide relative to an apparatus component, particlesmay still be produced, as the end of the shaft may rub against the rimof the tolerance ring during assembly owing to the tight fit between thetolerance ring and the shaft.

Alternatively, it may be advantageous to fit a tolerance ring withinward protrusions to the shaft, and insert the shaft and tolerance ringinto the bore. Although the inward protrusions do not rub against thesurface of the bore, particles may be produced when the rim of thetolerance ring rubs against the edge of the bore in the housing, owingto the tight fit between the ring and the housing.

The need to reduce or eliminate particle production can therefore imposerestrictions on the type of tolerance ring used. The tolerance ring thatminimizes particle production may not be the best choice for operationof the apparatus.

SUMMARY

Therefore, at its most general, the present invention proposes that thetolerance ring has a guide portion defining a surface inclined relativeto the axis of the tolerance ring which can act as a guide when thetolerance ring is inserted in a bore or when a shaft is mounted in thetolerance ring. In the former case, the surface will be inclinedoutwardly whereas in the latter case it will be inclined inwardly. Ineither situation, the guide portion assists the assembly of the variouscomponents, but reduces or eliminates particle production.

Thus, according to a first aspect of the invention, there may beprovided a tolerance ring comprising a band of resilient material havingcorrugated protrusions extending either radially outwards from the bandor radially inwards towards the axis of the band; and a guide portioncontiguous with, and extending axially from the band, wherein guideportion comprises at least one guide surface inclined relative to theaxis of the band such that the guide free end of the guide portion iswider than the opening of the band when the corrugated protrusionsextend radially outwards, and is narrower than the opening of the bandwhen the corrugated protrusions extend radially inwards.

The angle of inclination of the at least one guide surface relative tothe axis may be constant along the length of the guide surface, so thatthe guide surface defines the major part of a frusto-cone.Alternatively, the angle of inclination may change so that the guidesurface is curved in an axial section.

An advantage of the present invention is correct assembly of a ring in abore despite some axial misalignment of the ring and the bore.

The tolerance ring may be made of any suitable resilient material,preferably a metal, most preferably spring steel.

The guide portion may extend from the whole circumference of the band ofthe ring. Alternatively, the guide portion may extend from at least onesegment of the circumference of the tolerance ring. The guide surfacesof the guide portion may be flared relative to the inside surface of theband of the tolerance ring. In one embodiment, the guide surface flaresfrom the band to define an entrance at one end of the tolerance ring,wherein the perimeter or circumference of the entrance is greater thanthe circumference of the band of the tolerance ring. The guide portionprovides a funnel extending from the band of the ring, with the guidesurfaces angled relative to the axis of the band.

Conveniently, the guide surfaces of the guide portion are sufficientlyfree of obstruction so as to guide a shaft inserted axially into theguide portion into the band. If there is axial misalignment of the shaftand the axis of the tolerance ring, the guide surfaces of the guideportion serve to align axially the shaft with the band as the shaft isinserted into the band. The guide portion may include walls that aresubstantially parallel to the axis of the ring, for example near to theentrance.

Preferably, the entrance of the guide portion is circular or ovalshaped. The entrance may be concentric with the band. The entrance maybe rectangular or square in shape.

Preferably, the plane of the entrance is substantially perpendicular tothe axis of the tolerance ring. Alternatively, the plane of the openingmay be slanted relative to the axis of the ring, and a segment of theentrance is axially closer to the band than the rest of the entrance.

Alternatively, the guide surfaces of the guide portion taper towards theaxis of the ring to narrow or close the opening of the band. The guidesurfaces are provided by the outside surfaces of the guide portion.Ideally, the guide surfaces are sufficiently free of obstruction so asto allow the tolerance ring to be guided into a bore of a housing suchthat the bore of the housing is concentric with the band of thetolerance ring.

Ideally, the guide surface of any guide portion of the present inventionis sufficiently smooth to prevent the production of particles when theguide surface rubs or slides against a shaft and/or the entrance to abore in a housing. A possible advantage of the present invention istherefore a reduction in the particles normally generated when thetolerance ring is inserted inside a bore and/or fitted onto otherapparatus, such as a shaft.

The tolerance ring of the present invention is particularly suited toapparatus where particle production is undesirable, for example the harddisk drive of a computer. Additionally, or alternatively, the presentinvention may be particularly useful where it is advantageous todistribute tolerance ring loading over as wide an area as possible on acomponent that has to be inserted into or over the tolerance ring.

Such an apparatus may comprise a housing, which includes a bore, inwhich bore a tolerance ring of the first aspect of the present inventionis fitted such that the band of the tolerance ring is concentric withthe bore and the guide portion extends and flares towards the mouth ofthe bore. The protrusions of the ring preferably extend radiallyoutwards to engage the surface of the bore. A shaft can be inserted intothe ring via the entrance provided by the guide portion, to be grippedby the ring. The internal diameter of the band is suitable to grip theshaft. Ideally, the internal diameter of the band is substantially thesame as the diameter of the shaft.

The perimeter or circumference of the opening may be of sufficientdimension(s) to allow the opening to be accommodated inside the bore, sothat no part of the guide portion protrudes out of the housing.

Alternatively part of, or the entire, guide portion may reside outsideof the housing when the ring is in use, owing to the dimension(s) of theopening and/or the axial length of the guide portion. Alternatively, theguide portion may reside inside the housing such that the entrance ofthe guide portion lies flush with the outside of the housing.Preferably, the entrance of the guide portion is the same dimension andshape as the mouth of the bore.

The housing may be an actuator arm of a hard disk drive. The actuatorarm may pivot relative to a bearing or bearing assembly.

The apparatus may comprise a shaft, onto which a tolerance ring of thepresent invention is fitted, wherein the protrusions of the ringpreferably extend radially inwards. The tolerance ring may be fitted tothe periphery of the shaft such that the protrusions engage and grip theshaft. The guide portion extends axially, away from the end of theshaft, and tapers to narrow or close the opening of the band. The guideportion preferably narrows the opening of the band but preferably doesnot taper to a point. Alternatively, the guide portion may taper to apoint so that the tolerance ring acts a cap over the end of the shaft.Regardless of the exact shape of the guide portion, the guide surfacesof the guide portion allow the ring (and shaft) to be inserted into thebore of a housing such that the band of the tolerance ring sitsconcentrically in the bore. The external diameter of the band issufficient to create a snug fit between the band and the bore. Ideallythe external diameter of the band is substantially the same as thediameter of the bore.

Alternatively the apparatus may comprise a housing having a bore, ashaft and a tolerance ring of the first aspect of the invention, whereinat least part of the shaft is located in the bore and the band of thetolerance ring is concentrically located between the part of the shaftin the bore and the surface of the bore.

Preferably the apparatus is a hard disk drive and the shaft is a bearingor bearing assembly and the housing is an actuator arm. Preferably, theactuator arm pivots around the bearing or bearing assembly. Preferablythe bearing or bearing assembly remains stationary.

Alternatively, the apparatus may be a torque limiting apparatus such asEPAS or a steering column lock, where slip occurs between the ring andanother surface, an electric generator, a centrifugal pump, an airblower, a fan, a crane, woodworking or spinning machinery, a machinetool, a shaker or crusher.

The apparatus may be assembled by fitting a tolerance ring of the firstaspect of the invention to a shaft, so that the inwardly extendingprotrusions of the ring grip the shaft and the guide portion tapers awayfrom the shaft, the guide portion narrowing or closing the opening ofthe band; and inserting the shaft and ring into the bore of the housingsuch that the guide portion axially leads into the bore, such that theshaft/tolerance ring sits concentrically inside the bore and the band issufficiently dimensioned to allow a tight fit between the band and thesurface of the bore.

The guide surfaces of the guide portion may correct any axialmisalignment between the shaft/ring and the bore.

Alternatively, the apparatus may be assembled by fitting a tolerancering of the first or second aspect of the invention into a bore of ahousing such that the outwardly extending protrusions of the tolerancering contact the surface of the housing, wherein the band of thetolerance ring is suitably dimensioned to receive and grip a shaft, andthe guide portion extends towards the entrance of the bore, the guideportion widening the opening of the band; and inserting a shaft into theguide portion such that the shaft slides into the band/bore to implementan interference fit between the ring and the shaft.

The guide surface(s) of the guide portion may correct any axialmisalignment between the shaft and the tolerance ring/bore.

There may be a chamfer or flare at the mouth of the bore relative to thesides of the main section of the bore. This chamfer may act as a furtherguide, particularly in embodiments which the tolerance ring is mountedon a shaft prior to insertion in the bore. Such chamfers are, inthemselves, already known.

A further aspect of the invention provides a blank for making tolerancering of the first aspect. The blank comprises a strip of resilientmaterial, in which the corrugated protrusions are formed, and having theguide portion inclined relative to the plane of the rest of the strip.The resulting blank may subsequently be curved into a substantially anannular shape corresponding to the tolerance ring of the first aspectwith a gap between the ends of the strip.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detail, byway of example, reference to the accompanying drawings, in which:

FIG. 1 shows in cross section a bearing and a known tolerance ring,which are about to be inserted into a bore in a pivotable actuator armof a hard disk drive;

FIG. 2 shows in cross section another known tolerance ring with outwardprotrusions located in a bore in an actuator arm, and a bearing ready tobe inserted into the tolerance ring;

FIG. 3 shows in cross section another known tolerance ring with inwardprotrusions located in a bore in an actuator arm, and a bearing ready tobe inserted into the tolerance ring;

FIG. 4 shows in cross section a tolerance ring of the present inventionlocated in a bore in an actuator arm, and a bearing ready to be insertedinto the tolerance ring;

FIG. 5 shows in cross section, another known tolerance ring which isfitted to the end of a shaft and is about to be inserted into a bore ina housing; and

FIG. 6 shows in cross section a tolerance ring of the present invention,which is fitted to a shaft and is about to be inserted in a bore into ahousing.

DETAILED DESCRIPTION

Before describing embodiments of the invention, it will be useful tounderstand conventional arrangements. Thus, FIGS. 1 to 3 illustrate useof a known tolerance ring to mount a shaft in a bore.

Thus, as shown in FIG. 1, a known tolerance ring with outwardly facingprotrusions 2 in the form of waves and is fitted around a bearing 3 orbearing assembly 3 (hereinafter referred to as the bearing 3). Thebearing 3 and tolerance ring 1 comprise a sub-assembly, which is axiallyinserted into the bore 4 of a body which may be an actuator arm 5 of ahard disk drive, indicated in FIG. 1 by the arrow 6. Unformed, annularportions 7 of the tolerance ring 1, which have no radial protrusions,axially flank the outwardly facing protrusions 2. Tolerance rings withoutwardly facing protrusions are generally known in the art as S.V rings(Shaft Variable), as the diameter of the tolerance ring to be fitted tothe bearing may be varied by differing amounts of overlap of the ends ofthe strip that forms the tolerance ring. The outwardly facingprotrusions 2 of the ring 1 resiliently engage the surface 8 of the bore4.

As the sub-assembly is inserted into the bore 4, the outwardly facingprotrusions 2 of the tolerance ring 1 are compressed. Unformed portions7 of the tolerance ring 1 that axially flank the outwardly facingprotrusions 2 prevent changes in the pitch of the outwardly facingprotrusions 2, allowing only resilient deformation of each outwardlyfacing protrusions. A radial force is created between the surface 8 ofthe bore 4 and the bearing 3. An interference fit is thus provided bythe tolerance ring 1.

During assembly, the outwardly facing protrusions 2 of the tolerancering 1 slide relative to the surface 8 of the bore 4. Abrasion of thewaves against the surface 8 can cause small fragments of the housing 5to be removed from the surface 8 of the bore 4 (and possibly tolerancering 1). This problem is compounded if the material of the actuator arm5 is softer than the material of the outwardly facing protrusions 2 ofthe ring 1. The fragments are known in the art as particles, which canadversely affect the operation of the apparatus in which the tolerancering 1 is fitted. In the example, particles are extremely undesirable ascleanliness is important for proper functioning of the hard disk drive.

An alternative known assembly method comprises inserting the tolerancering 1 into the bore 4 so that the tolerance ring 1 sits concentricallyin the bore 4. The bearing 3 is inserted into the bore 4 and slides intothe tolerance ring 1, as shown by the arrow 9 in FIG. 2. The bearing 3may foul on the edge 10 of the ring as the bearing 3 is axially insertedinto the ring 1, causing fragments of the ring 1 and/or bearing 3 to beremoved. The fragments are known in the art as particles.

Particles may also be produced when using a tolerance ring with inwardlyextending protrusions, for example as shown FIG. 3. A tolerance ring 11,with inwardly facing protrusions 30, sits concentrically in the bore 4of the actuator arm 5, with the sides of the ring engaging the sides 8of the bore 4. This type of ring is known in the art as an H.V.tolerance ring (Housing Variable). A bearing 3 is axially inserted intothe ring 11, as indicated in FIG. 3 by the arrow 12. The bearing 3 movesrelative to the inwardly facing protrusions 30. As the bearing 3 is madeof harder material than the actuator arm 5, particle production is morelimited.

The arrangement using a tolerance ring with inwardly extending waves maynot be suitable for all types of apparatus, for example where it isdesirable to have a load on the bearing spread over a wider area thancan be provided by the tops of the waves. It is undesirable that arequirement to minimise particle production during assembly imposes aworking arrangement that is sub-optimal for the apparatus.

In a computer hard disk drive the arrangement using a tolerance ringwith inwardly extending waves (H.V) is undesirable, as load must bespread over as wide an area of the bearing as possible to avoid torqueripple. Furthermore, axial alignment, required in a hard disk drive, isusually better with tolerance rings having outwardly extending waves(S.V), shown in FIGS. 1 and 2. However, manufacturers may use the H.Vring and assembly method described in Example 3, as it minimizesparticle production during assembly. Particles will adversely affect thefunctioning of the hard disk drive.

As had previously been mentioned, a tolerance ring according to thepresent invention modifies known tolerance rings by providing a guideportion which is inclined relative to the axis of the tolerance ring.The first embodiment of the present invention will now be described withreference to FIG. 4. Some of the features of the tolerance ring of thisembodiment are the same in the tolerance rings described previously, andthe same reference numerals will be used to indicate correspondingparts.

A tolerance ring 13 being the first embodiment of the present inventionallows a tolerance ring with outwardly facing protrusions 2 to be usedin the apparatus but minimizes or eliminates the particle productionthat results from the arrangements shown in FIGS. 1, 2 and 3. Thetolerance ring 13 includes a guide portion indicated generally in FIG. 4by 14. The guide portion 14 resembles a funnel, which flares towards theentrance of the bore 4. The guide portion comprises a flared guidesurface, indicated in cross section by 15 in FIG. 4, extending axiallyfrom the band 16 of the ring 13, forming an endmost annular portion,towards the entrance of the bore 4. The guide portion terminates at freeend 32 defining an axial end of the tolerance ring. This free end 32defines an opening that (i) is larger than that defined by the unformedannular portions of the band, and (ii) has a diameter at said free endthat is not greater than the diameter of the protrusions. As shown, theguide portion is provided at only one end of the band.

The guide surface 15 provides an enlarged entrance to the band 16 of thering 13 for receiving the bearing, eliminating foul on the edge of thering as described in Example 2. Guide surface 15 is sufficiently smoothso as to guide the bearing 3 into the ring 13, even if there is someaxial misalignment of the bearing 3 and the ring 13. As the outwardlyfacing protrusions 2 of the ring 13 do not abrade against any surfaceduring assembly and the end of the bearing 3 does not abrade against thering 13, particle production is avoided. As shown, the tolerance ring 13in the form of an annular band of resilient material has an innermostsurface defined by the unformed annular portions 7, and has an outermostsurface defined by the outwardly facing protrusions 2 having a diameter.All of the outwardly facing protrusions 2 extend radially outward, eachextending between a pair of unformed annular portions. The guide portionis contiguous with and extends axially and radially outward from anendmost unformed annular portion (the topmost unformed annular portionshown in FIG. 4), and flares outwardly from the innermost surface. Asshown, the guide portion has a free end defining an opening that has adiameter not greater than the diameter of the unformed annular portions.The arrangement using an S.V. type ring is preferable for the hard diskdrive.

It is also known to use a tolerance ring with inwardly facingprotrusions. The ring may be fitted to the end of a shaft and insertedinto a bore in the housing, as shown in FIG. 5. The tolerance ring 17,with inwardly facing protrusions 2, is fitted to a shaft 18 and theshaft 18 and ring 17 inserted axially into the bore 4 of a housing 19.The diameter of the ring 17 is similar to the diameter of the bore 4 andso the ring 17 fouls on the edge 20 of the bore 4, producing particlesfrom the ring 17 and/or the housing 19.

This known tolerance ring can be modified by the provision of aninclined guide portion, in a manner similar to the first embodiment, butwith the angle of inclination being inward rather than outward. Such anembodiment is illustrated in FIG. 6, and again reference numerals areused to indicate corresponding parts. Tolerance ring 21 of the secondembodiment is fitted to a shaft 18, and axially inserted into the bore 4of a housing 19. The ring 21 includes inward protrusions in the form ofwaves to the grip shaft 18.

The ring includes a tapered guide portion indicated generally in FIG. 6by 22, extending axially from the band 23 of the ring, away from theshaft 18. The guide portion comprises a guide surface, indicated incross section in FIG. 6 by 24 a, sloping towards the axis of the ring tonarrow the opening of the band 23. The guide surface 24 a axially leadsinto the bore 4 during assembly. The guide surface allows correction ofaxial misalignment of the bearing and the bore. The guide portionprevents the ring fouling on the edge of the bore 20, reducing or eveneliminating particle production.

In the embodiments described above, the bore 4 has straight side walls.It is possible for the ends of the bore to be chamfered, although thepresence of the guide portion makes such chamfering of little benefit.

The tolerance ring of the invention may be used on a hard disk drive,although there are numerous other applications of the present invention,for example any apparatus that uses a tolerance ring. In the example,the hard disk drive has an actuator arm pivotable around a bearing orbearing assembly. Typically, the actuator arm has an electronictransducer at one end for reading and writing data stored on a mediadisk. The arm pivots around a stationary shaft, which is mountedperpendicular to the plane of rotation of the media disk and arm.

Conventionally, the pivot mechanism comprises a centre shaft and one ora plurality of rolling element bearings surrounding the shaft. Eachrolling element bearing includes an inner race attached to the shaft, anouter race located concentrically around the inner race, and a pluralityof rolling elements located in the annular space between the inner andouter races. Such an assembly is commonly known as a bearing cartridgeassembly. An outer cylinder or sleeve may surround the outer race orraces of the bearing or bearings. Although such a hard disk drive is atypical arrangement, it will be appreciated by those in the art thatthere are other possible arrangements to which the invention can beapplied.

What is claimed is:
 1. A tolerance ring having a first axial end, asecond axial end, and a central axis, the tolerance ring comprising: anannular band; a plurality of protrusions, all of the plurality ofprotrusions extending from the annular band; and a guide portionextending from the annular band towards the first axial end of thetolerance ring, wherein the guide portion comprises a guide surface thatis curved in an axial section.
 2. The tolerance ring according to claim1, wherein the annular band defines an annular segment disposed betweenthe guide portion and the plurality of protrusions.
 3. The tolerancering according to claim 2, wherein the guide portion comprises a minimumdiameter, and wherein the minimum diameter of the guide portion iscoincident with the annular segment.
 4. The tolerance ring according toclaim 1, wherein the annular band is adapted to contact a bearing. 5.The tolerance ring according to claim 1, wherein the annular band isadapted to contact a shaft.
 6. The tolerance ring according to claim 1,wherein the guide portion is visible when viewed from the first axialend along the central axis of the tolerance ring.
 7. The tolerance ringaccording to claim 1, wherein the plurality of protrusions extendradially outwards from the annular band.
 8. The tolerance ring accordingto claim 1, wherein the plurality of protrusions extend radially inwardsfrom the annular band.
 9. The tolerance ring according to claim 1,wherein the guide portion extends along a whole circumference of theannular band.
 10. An apparatus comprising: a housing having a boretherein; a shaft in the bore; and a tolerance ring positioned betweenthe interior surface of the bore and the external surface of thehousing, the tolerance ring comprising: an annular band; a plurality ofprotrusions, all of the plurality of protrusions extending from theannular band; and a guide portion extending from the annular bandtowards the first axial end of the tolerance ring, wherein the guideportion comprises a guide surface that is curved in an axial section ofthe guide portion is visible when viewed from the first axial end alongthe central axis of the tolerance ring.
 11. The tolerance ring accordingto claim 10, wherein the annular band defines an annular segmentdisposed between the guide portion and the plurality of protrusions. 12.The tolerance ring according to claim 11, wherein the guide portioncomprises a minimum diameter, and wherein the minimum diameter of theguide portion is coincident with the annular segment.
 13. The tolerancering according to claim 10, wherein all of a guide surface of the guideportion is visible when viewed along a central axis of the tolerancering.
 14. The tolerance ring according to claim 10, wherein the guideportion extends along a whole circumference of the annular band.
 15. Amethod of assembling an apparatus, comprising: inserting a tolerancering into a bore in a housing, the tolerance ring comprising: an annularband; a plurality of protrusions, all of the plurality of protrusionsextending from the annular band; and a guide portion extending from theannular band towards the first axial end of the tolerance ring, whereinthe guide portion comprises a guide surface that is curved in an axialsection of the guide portion is visible when viewed from the first axialend along the central axis of the tolerance ring; and inserting an endof a shaft into the guide portion of the tolerance ring; and moving theshaft along the axis of the band into the band, so that the band engagesthe shaft.
 16. The method according to claim 15, wherein all of a guidesurface of the guide portion is visible when viewed along a central axisof the tolerance ring.
 17. The method according to claim 15, wherein theguide portion extends along a whole circumference of the annular band.18. The method according to claim 15, wherein the annular band definesan annular segment disposed between the guide portion and the pluralityof protrusions.
 19. The method according to claim 18, wherein the guideportion comprises a minimum diameter, and wherein the minimum diameterof the guide portion is coincident with the annular segment.
 20. Themethod according to claim 15, wherein the plurality of protrusionsextend radially outwards from the annular band.